#app4 {
}
#app4 .circle {
  border: 3px solid pink;
  width: 25vh;
  height: 25vh;
  border-radius: 50%;
}
@keyframes change {
  0% {
    background-color: blue;
  }
  100% {
    background-color: red;
  }
}
/* #app4 .circle:hover {
  animation: change 3s infinite alternate;
} */
#app4 .circle.active {
  animation: change 3s infinite alternate;
}
